The term El Niño (Spanish for
"the little boy" or "the Christ Child") was originally used by fishermen
along the coasts of Ecuador and Peru to refer to above-normal
sea-surface temperatures that typically appear around Christmastime in
the eastern Pacific Ocean and last for several months.

How Does El Niño Work?

In normal years, the winds tend to blow
from east to west across the waters of the tropical Pacific. The easterly winds push the surface
waters westward across the ocean. In turn, this causes deeper, colder
waters to rise to the surface. This "upwelling" of deep ocean waters
brings with it the nutrients that otherwise would remain near the
bottom. The fish populations living in the upper waters are dependent on
these nutrients for survival.

During El Niño years, the winds weaken, causing the
upwelling of deep water to cease. The consequent warming of the ocean surface further
weakens the winds and strengthens El Niño. As the ocean warms, the
warmer water shifts eastward and so do the clouds and thunderstorms that
produce heavy rainfall along the equator. This results in changes in jet
streams (winds aloft), which lead to dry conditions in Indonesia and
Australia, and floods in Peru and Ecuador. El Niño events occur on
average every 3 to 5 years.

El Niño's Effects

The 1982-83 El Niño was
unusually strong. In Ecuador and northern
Peru, up to 100 inches of rain fell during a six-month period,
transforming the coastal desert into a grass-land dotted with lakes.
Abnormal wind patterns also caused the monsoon rains to fall over the
central Pacific instead of on the western edge, which led to droughts
and disastrous forest fires in Indonesia and Australia. Overall, the
loss to the global economy as a result of the El Niño amounted to more
than $8 billion.

Likewise, the winter of 1997-1998 was marked by a
record-breaking El Niño event. The result was unusual weather in parts of the world,
including the U.S. Severe weather events included flooding in the
southeastern United States, major storms in the Northeast, and flooding
in California.

La Niña

El Niño's twin
sister is La Niña ("the little girl" in Spanish). La Niña is characterized
by below-normal sea surface temperatures in the eastern equatorial Pacific. There are large swings in weather
for many U.S. locations from warm spells to cold waves during a La Niña winter.
The effects of La Niña tend to be nearly the opposite of El Niño for
instance, precipitation is below normal in California and the
southeastern U.S.

El Niño and Global Warming: Any Connection?

Scientists still
cannot say with certainty that global warming is affecting El Niño events. In January 1999, however, scientists
at the National Center for Atmospheric Research and elsewhere reported that
global warming may accentuate El Niño's current and future impacts. El
Niño events have become more frequent and have had greater climate
impacts over the past century. This change in El Niño events corresponds
to a rise in global temperatures.